Security of two-way quantum cryptography against asymmetric Gaussian attacks

Recently, we have shown the advantages of two-way quantum communications in continuous variable quantum cryptography. Thanks to this new approach, two honest users can achieve a non-trivial security enhancement as long as the Gaussian interactions of an eavesdropper are independent and identical. In this work, we consider asymmetric strategies where the Gaussian interactions can be different and classically correlated. For several attacks of this kind, we prove that the enhancement of security still holds when the two-way protocols are used in direct reconciliation.Comment: Proceeding of the SPIE Conference "Quantum Communications and Quantum Imaging VI" - San Diego 2008. This paper is connected with arXiv:quant-ph/0611167 (for the last version see: Nature Physics 4, 726 (2008)

Confidential direct communications: a quantum approach using continuous variables

We consider the problem of privacy in direct communications, showing how quantum mechanics can be useful to guarantee a certain level of confidentiality. In particular, we review a continuous variable approach recently proposed by us [S. Pirandola et al., Europhys. Lett. 84, 20013 (2008)]. Here, we analyze the degree of privacy of this technique against a broader class of attacks, which includes non-Gaussian eavesdropping.Comment: Invited paper. Extension of results presented in arXiv:0802.0656 (REVTeX, 11 pages, 11 figures

Causal reasoning about distributed programs

We present an integrated approach to the specification, verification and testing of distributed programs. We show how global properties defined by transition axiom specifications can be interpreted as definitions of causal relationships between process states. We explain why reasoning about causal rather than global relationships yields a clearer picture of distributed processing.;We present a proof system for showing the partial correctness of CSP programs that places strict restrictions on assertions. It admits no global assertions. A process annotation may reference only local state. Glue predicates relate pairs of process states at points of interprocess communication. No assertion references auxiliary variables; appropriate use of control predicates and vector clock values eliminates the need for them. Our proof system emphasizes causality. We do not prove processes correct in isolation. We instead track causality as we write our annotations. When we come to a send or receive, we consider all the statements that could communicate with it, and use the semantics of CSP message passing to derive its postcondition. We show that our CSP proof system is sound and relatively complete, and that we need only recursive assertions to prove that any program in our fragment of CSP is partially correct. Our proof system is, therefore, as powerful as other proof systems for CSP.;We extend our work to develop proof systems for asynchronous communication. For each proof system, our motivation is to be able to write proofs that show that code satisfies its specification, while making only assertions we can use to define the aspects of process state that we should trace during test runs, and check during postmortem analysis. We can trace the assertions we make without having to modify program code or add synchronization or message passing.;Why, if we verify correctness, would we want to test? We observe that a proof, like a program, is susceptible to error. By tracing and analyzing program state during testing, we can build our confidence that our proof is valid

The Quantum Vacuum Near Time-Dependent Dielectrics

The vacuum, as described by Quantum Field Theory, is not as empty as classical physics once led us to believe. In fact, it is characterised by an infinite energy stored in the ground state of its constituent fields. This infinite energy has real, tangible effects on the macroscopic clusters of matter that make up our universe. Moreover, the configuration of these clusters of matter within the vacuum in turn influences the form of the vacuum itself and so forth. In this work, we shall consider the changes to the quantum vacuum brought about by the presence of time-dependent dielectrics. Such changes are thought to be responsible for phenomena such as the simple and dynamical Casimir effects and Quantum Friction. After introducing the physical and mathematical descriptions of the electromagnetic quantum vacuum, we will begin by discussing some of the basic quasi-static effects that stem directly from the existence of an electromagnetic ground state energy, known as the \textit{zero-point energy}. These effects include the famous Hawking radiation and Unruh effect amongst others. We will then use a scenario similar to that which exhibits Cherenkov radiation in order to de-mystify the 'negative frequency' modes of light that often occur due to a Doppler shift in the presence of media moving at a constant velocity by showing that they are an artefact of the approximation of the degrees of freedom of matter to a macroscopic permittivity function. Here, absorption and dissipation of electromagnetic energy will be ignored for simplicity. The dynamics of an oscillator placed within this moving medium will then be considered and we will show that when the motion exceeds the speed of light in the dielectric, the oscillator will begin to absorb energy from the medium. It will be shown that this is due to the reversal of the 'radiation damping' present for lower velocity of stationary cases. We will then consider how the infinite vacuum energy changes in the vicinity, but outside, of this medium moving with a constant velocity and show that the presence of matter removes certain symmetries present in empty space leading to transfers of energy between moving bodies mediated by the electromagnetic field. Following on from this, we will then extend our considerations by including the dissipation and dispersion of electromagnetic energy within magneto-dielectrics by using a canonically quantised model referred to as 'Macroscopic QED'. We will analyse the change to the vacuum state of the electromagnetic field brought about by the presence of media with an arbitrary time dependence. It will be shown that this leads to the creation of particles tantamount to exciting the degrees of freedom of both the medium and the electromagnetic field. We will also consider the effect these time-dependencies have on the two point functions of the field amplitudes using the example of the electric field. Finally, we will begin the application of the macroscopic QED model to the path integral methods of quantum field theory with the purpose of making use of the full range of perturbative techniques that this entails, leaving the remainder of this adaptation for future work.EPSR

I'm Scared

I’m Scared.Last week I watched as every theater company in the country shut down. I wash myhands every hour or so. I’m down to the last roll of toilet paper. I scroll the internet for updateson an epidemic that will define my transition from student to artist.In this tense moment I find new reverence for the formalized ritual of gathering togetherto watch live theater. The anxiety of social distancing reminds me that people crave connectionthrough shared experience. We want to be in one big room with each other. As a theater-maker,this fundamental desire for proximity reminds me of why I love the performing arts.In a few months this pandemic will be behind us, and theater artists will be on the frontline teaching the public how to be together again. In the mean time I’ll search for ways to feelcloseness, and to help others feel closeness, even when while quarantined in my hom

Optimality of Gaussian Discord

In this Letter we exploit the recently-solved conjecture on the bosonic minimum output entropy to show the optimality of Gaussian discord, so that the computation of quantum discord for bipartite Gaussian states can be restricted to local Gaussian measurements. We prove such optimality for a large family of Gaussian states, including all two-mode squeezed thermal states, which are the most typical Gaussian states realized in experiments. Our family also includes other types of Gaussian states and spans their entire set in a suitable limit where they become Choi-matrices of Gaussian channels. As a result, we completely characterize the quantum correlations possessed by some of the most important bosonic states in quantum optics and quantum information.Comment: ReVTEX. 4 pages + 6 pages (Supplemental Material

Characterization of Collective Gaussian Attacks and Security of Coherent-State Quantum Cryptography

We provide a simple description of the most general collective Gaussian attack in continuous-variable quantum cryptography. In the scenario of such general attacks, we analyze the asymptotic secret-key rates which are achievable with coherent states, joint measurements of the quadratures and one-way classical communication.Comment: 4 pages, 1 figure + 1 Table, REVteX. More descriptive titl

Parameter Estimation and Uncertainty Quantication for an Epidemic Model

We examine estimation of the parameters of Susceptible-Infective-Recovered (SIR) models in the context of least squares. We review the use of asymptotic statistical theory and sensitivity analysis to obtain measures of uncertainty for estimates of the model parameters and the basic reproductive number (R0 )—an epidemiologically significant parameter grouping. We find that estimates of different parameters, such as the transmission parameter and recovery rate, are correlated, with the magnitude and sign of this correlation depending on the value of R0. Situations are highlighted in which this correlation allows R0 to be estimated with greater ease than its constituent parameters. Implications of correlation for parameter identifiability are discussed. Uncertainty estimates and sensitivity analysis are used to investigate how the frequency at which data is sampled affects the estimation process and how the accuracy and uncertainty of estimates improves as data is collected over the course of an outbreak. We assess the informativeness of individual data points in a given time series to determine when more frequent sampling (if possible) would prove to be most beneficial to the estimation process. This technique can be used to design data sampling schemes in more general contexts

Methane, hydrogen and carbon dioxide production in the digestive tract of ruminants in relation to the respiratory exchange.

Publication authorized May 28, 1937."This bulletin is based on a dissertation by Lloyd Eugene Washington presented in May, 1937 to the Graduate School of the University of Missouri in partial fulfillment of the requirements for the degree of Doctor of Philosophy"--P. [5].Includes bibliographical references (pages 38-40)